In any emergency or hit the fan scenerio, your mental stress levels will rise and your diet won’t be what your system is used to which might lead to constipation. Keeping well hydrated and eating fresh high fiber foods but those may be in limited supply. So, add to your medicine cabinet acidophilous tablets and magnesium citrate.
Yogurt is simple to make (heat source, milk product, starter) but make sure your starter contains live cultures. A few spoonfuls of yogurt can be saved as your starter for up to 4 future batches.
A jug of Apple Cider Vinegar will do all and more for balancing the system.